The short version of accuracy fits in a sentence. The long version — which is the one that helps — is below.
This page was last updated on 2025-10-03 and is reviewed periodically as new material appears.
Method validation establishes that an HPLC procedure is suitable for its intended purpose. Typical parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantitation, robustness, and solution stability. Accuracy reflects closeness to a reference value, while precision reflects agreement among repeated measurements. Specificity shows whether the method can measure the analyte without interference from matrix components. Validation is documented through protocols and reports, and the required extent depends on the method's use and regulatory context.
Routine quality control uses system suitability, blank injections, check standards, and control samples to detect drift or contamination. System suitability criteria may specify minimum resolution, maximum tailing factor, and a permitted range for repeated injections. Blank injections reveal carryover or solvent contamination, while check standards confirm calibration accuracy over a batch. Control samples with known analyte levels can show whether results remain within statistical limits. When a control result falls outside limits, the analyst investigates the cause and may invalidate affected results before repeating the batch.
Method validation demonstrates that an HPLC procedure is suitable for its intended purpose. Common validation parameters include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantification, and robustness. Accuracy reflects agreement with a reference value, while precision describes repeatability under defined conditions. Specificity shows whether the method can measure the analyte in the presence of impurities or matrix components. Validation documents are reviewed before a method is used for routine testing or regulatory submissions.
System suitability testing is performed before and during analytical runs to confirm that the instrument and method are working as expected. Typical checks include retention time, peak area precision, resolution between critical pairs, tailing factor, and theoretical plate count. Acceptance criteria are set in the method or pharmacopeial monograph. If a suitability check fails, the run may be rejected and the instrument or sample preparation may need investigation. This practice helps prevent release of data from a system that has drifted out of control.
Quality control samples are inserted at intervals to monitor accuracy and precision throughout a batch. Blank samples detect contamination, while spiked samples assess recovery from the sample matrix. Calibration standards establish the relationship between detector response and concentration, and control samples are prepared independently from them whenever possible. Laboratories also participate in proficiency testing and maintain audit trails, instrument logs, and reagent records. Ongoing review of control charts can reveal trends before they cause out-of-specification results.
| Property | Value | Notes |
|---|---|---|
| Accuracy | Recovery near 100% | Depends on acceptance criteria and matrix |
| Precision | Relative standard deviation | Often at or below 2% for replicate injections |
| Limit of detection | Signal-to-noise ratio 3:1 | Approximate and method-specific |
| Limit of quantitation | Signal-to-noise ratio 10:1 | Confirmed by precision and accuracy |
| Resolution | 1.5 or greater | Typical system suitability target |
Developing an HPLC method begins with defining the purpose, such as quantifying a main component, measuring impurities, or confirming identity. Analysts select separation mode, column, mobile phase, detection, and sample preparation based on analyte properties and matrix. Experiments vary solvent strength, pH, buffer type, and temperature to achieve resolution between critical peaks. The goal is a robust method that produces reliable results across instruments and operators. Method development often involves trial runs and statistical optimization.
Validation demonstrates that a method is suitable for its intended use. Typical performance characteristics include accuracy, precision, specificity, linearity, range, limit of detection, limit of quantitation, and robustness. Regulators and standards organizations provide frameworks, but specific requirements depend on the application and jurisdiction. System suitability tests are run before sample analysis to confirm resolution, peak symmetry, retention time repeatability, and sensitivity. A validated method is not permanently fixed; changes may require partial or full revalidation.
System suitability testing is performed before and during analytical runs to confirm that the instrument and method are working as expected. Common checks include retention time, peak area, resolution between critical pairs, tailing factor, and theoretical plate count. Results are compared with predefined limits, and a failed check requires investigation before sample results are reported. Quality control samples at low, middle, and high concentrations are injected at intervals to monitor accuracy and precision. Blank injections detect carryover and contamination, while control charts track performance over time.
Data handling and documentation are central to HPLC quality control. Electronic systems should have audit trails that record changes to methods, sequences, and results. Integration parameters, such as peak baseline and threshold, can affect reported areas and must be defined in advance. Out-of-specification results trigger a structured investigation that may include reanalysis, instrument checks, and review of sample preparation. Regulatory inspections often examine raw data, audit trails, and training records to verify that reported results are traceable and reliable.
Key performance measures include retention time, peak area, peak height, resolution, tailing factor, and plate count. Retention time helps identify a peak under fixed conditions, but confirmation often requires a second method or detector. Peak area and height relate to concentration through calibration curves, which may be linear or nonlinear depending on the detector response. Resolution describes separation between adjacent peaks, while tailing factor and plate count describe peak shape and column efficiency. Performance checks verify these values before and during a run to confirm that the instrument is performing within limits.
High-performance liquid chromatography testing separates components of a liquid sample by forcing a mobile phase through a packed column. The stationary phase inside the column interacts with analytes to different degrees, so each compound exits at a characteristic retention time. A pump delivers solvent at controlled flow and pressure, while an injector introduces a precise sample volume. Detectors such as ultraviolet-visible, fluorescence, refractive index, or mass spectrometric instruments record the separated bands. The resulting chromatogram provides qualitative and quantitative information about the mixture.
Separation modes differ by the chemistry of the stationary phase and the composition of the mobile phase. Reversed-phase testing uses a nonpolar column and polar solvents, making it common for pharmaceutical, environmental, and food analytes. Normal-phase testing uses a polar column and nonpolar solvents for compounds that are poorly retained in reversed-phase systems. Ion-exchange and ion-pair methods separate charged species, while size-exclusion methods sort molecules by hydrodynamic volume. Gradient elution changes solvent strength over time to resolve complex mixtures, and isocratic elution holds solvent composition constant for simpler assays.
Instrumentation includes a solvent delivery system, an autosampler, a column oven, and one or more detectors. Reversed-phase columns with chemically modified silica are widely used, but normal-phase, ion-exchange, size-exclusion, and affinity modes exist for specific separations. Detectors may rely on ultraviolet absorbance, fluorescence, refractive index, or mass spectrometry. Column temperature, mobile phase composition, and flow rate are adjusted to improve resolution. System pressure is monitored because rising pressure can indicate column blockage or deteriorating packing.
Separation performance depends on particle size, pore size, column length, and the chemistry of the stationary phase. Smaller particles generally improve efficiency but require higher pressure and suitable instrumentation. The mobile phase often contains buffers and organic solvents that influence retention and selectivity. Testing labs select conditions based on the analytes, sample matrix, and required sensitivity. Method development frequently involves screening several columns and solvent mixtures before a final set of conditions is chosen.
Tropaeolum tuberosum (mashua, see below for other names) is a species of flowering plant in the family Tropaeolaceae, grown in the Andes, particularly in Peru and Bolivia, and to a lesser extent in Ecuador as well as in some areas of Colombia, for its edible tubers, which are eaten cooked or roasted as a vegetable. It is a minor food source, especially for native Amerindian populations. Mashua is a herbaceous perennial climber growing to 2–4 m (7–13 ft) in height. It is related to garden nasturtiums, and is occasionally cultivated as an ornamental for its brightly coloured tubular flowers. The leaves are peltate, roundly five-lobed with a petiole that twines weakly but is not truly a tendril. The root is tuberous.
==== "Depression Baby" ==== During the 1930s, the North American Car Company produced a one-of-a-kind, four-wheeled ice-bunker reefer intended to serve the needs of specialized shippers who did not generate enough product to fill a full-sized refrigerator car. NADX #10000 was a 22-foot (6.71 m)-long, all-steel car that resembled the forty-and-eights used in Europe during World War I. The prototype weighed 13.5 short tons (12.2 t; 12.1 long tons) and was outfitted with a 1,500 lb (680 kg) ice bunker at each end. The car was leased to Hormel and saw service between Chicago, Illinois and the southern United States. The concept failed to gain acceptance with eastern railroads, and no additional units were built.
Poole integrates into the society of 3001, but is prompted by a friend to revisit Europa, a cradle of nascent life from which the monolith had banned humanity almost a millennium earlier. It is believed he might be the first person allowed to visit there. On Europa he is greeted by the voice of David Bowman and computer HAL 9000, who have now become a single entity—Halman—residing as digitized lifeforms in the monolith's computational matrix. In subsequent conversations he learns that the monoliths themselves are mechanisms, answerable to an unknown superior monolith, or perhaps lifeforms, almost 450 light-years away. Thirty years later, Poole is married, and a member of a small team responsible for monitoring Europa. Halman contacts him to warn that following the events of 2010: Odyssey Two and 2061: Odyssey Three, the Jovian monolith had sent a report to its superior monolith, containing details about the human species after first contact. Since this report took place shortly after the wars of the 20th century, Halman believes the response just received after the 900-year round trip contains instructions to destroy humanity, due to its perceived failure as a species. Unsure whether they can physically harm the Monolith, the Europa team decide instead to infect it—as a computational mechanism—with a computer virus. Poole requests Halman to act as a Trojan Horse and place the virus inside the monolith, where it will be executed.
Sources: en.wikipedia.org
Correct functioning of agouti requires DNA methylation. Methylation occurs in six guanine-cytosine (GC) rich sequences in the 5’ long terminal repeat of the IAP element in the viable yellow mutation. Methylation on a gene causes the gene to not be expressed because it will cause the promoter to be turned off. In utero, the mother's diet can cause methylation or demethylation. When this area is unmethylated, ectopic expression of agouti occurs, and yellow phenotypes are shown because the phaeomelanin is expressed instead of eumelanin. When the region is methylated, agouti is expressed normally, and grey and brown phenotypes (eumelanin) occur. The epigenetic state of the IAP element is determined by the level of methylation, as individuals show a wide range of phenotypes based on their degree of DNA methylation. Increased methylation is correlated with increased expression of the normal agouti gene. Low levels of methylation can induce gene imprinting which results in offspring displaying consistent phenotypes to their parents, as ectopic expression of agouti is inherited through non-genomic mechanisms. DNA methylation is determined in utero by maternal nutrition and environmental exposure. Methyl is synthesized de novo but attained through the diet by folic acid, methionine, betaine, and choline, as these nutrients feed into a consistent metabolic pathway for methyl synthesis. Adequate zinc and vitamin B12 are required for methyl synthesis as they act as cofactors for transferring methyl groups.
=== Norwegian === According to Guinness Book of Records (2001), the longest meaningful word used in Norwegian is minoritetsladningsbærerdiffusjonskoeffisientmålingsapparatur (63 letters), meaning devices for measuring coefficients of diffusion of carriers of minority charges. Nouns, and also verbs and adjectives, can be prefixed as qualifiers to other words quite freely, e.g. to make an unlikely, but understandable and grammatically correct, compound word like damplokomotivfyrbøteraspirantluemerkeprodusentdatterkinoavtaletidspunkt, an agreed meeting time for a cinema date with a daughter of a producer of hat badges for trainees aiming to become firemen on steam locomotives.
==== Protein purification ==== Knowledge of an enzyme's resistance to high temperatures is especially beneficial in protein purification. In the procedure of heat denaturation, one can subject a mixture of proteins to high temperatures, which will result in the denaturation of proteins that are not thermostable, and the isolation of the protein that is thermodynamically stable. One notable example of this is found in the purification of alkaline phosphatase from the hyperthermophile Pyrococcus abyssi. This enzyme is known for being heat stable at temperatures greater than 95 °C, and therefore can be partially purified by heating when heterologously expressed in E. coli. The increase in temperature causes the E. coli proteins to precipitate, while the P. abyssi alkaline phosphatase remains stably in solution.
Sources: en.wikipedia.org
On October 7, 2001, U.S. and British forces initiated bombing campaigns that led to the arrival of Northern Alliance troops in Kabul on November 13. The main goals of the war were to defeat the Taliban, drive al-Qaeda out of Afghanistan, and capture key al-Qaeda leaders. In December 2001, the Pentagon reported that the Taliban had been defeated, but cautioned that the war would go on to continue weakening Taliban and al-Qaeda leaders. Later that month the UN had installed the Afghan Transitional Administration chaired by Hamid Karzai. Efforts to kill or capture al-Qaeda leader Osama bin Laden failed as he escaped a battle in December 2001 in the mountainous region of Tora Bora, which the Bush Administration later acknowledged to have resulted from a failure to commit enough U.S. ground troops. It was not until May 2011, two years after Bush left office, that Bin Laden was killed by U.S. forces under the Obama administration. Despite the initial success in driving the Taliban from power in Kabul, by early 2003 the Taliban was regrouping, amassing new funds and recruits. The 2005 failure of Operation Red Wings showed that the Taliban had returned. In 2006, the Taliban insurgency appeared larger, fiercer and better organized than expected, with large-scale allied offensives such as Operation Mountain Thrust attaining limited success. As a result, Bush deployed 3,500 additional troops to the country in March 2007.
=== Pharmacokinetics === Piperacillin is generally available in their stable form as crystallized potassium or sodium salt, quickly losing bactericidal activity upon dissolution due to their short half-lives. As the gastrointestinal tract does not absorb piperacillin and tazobactam, they are dissolved in a solution before being administered to a patient, through parenteral means. Excreted through renal mechanisms like glomerular or tubular filtration as a component of urine, uncontrolled dosages of the drug can cause renal dysfunction and competitive inhibition of excretion, delaying piperacillin-tazobactam excretion, and endangering patients to drug exposure.
Breast development starts in puberty with the growth of ducts, fat cells, and connective tissue. The ultimate size of the breasts is determined by the number of fat cells. The size of the breast is not related to a mother's breastfeeding capability or the volume of milk she can produce. The process of milk production, termed lactogenesis, occurs in 3 stages. The first stage takes place during pregnancy, allowing for the development of the breast and production of colostrum, the thick, early form of milk that is low in volume but rich in nutrition. The birth of the baby and the placenta trigger the onset of the second stage of milk production, triggering the milk to come in over the next several days. The third stage of milk production occurs gradually over several weeks and is characterized by a full milk supply that is regulated locally (at the breast), predominantly by the infant's demand for food. This differs from the second stage of lactogenesis, which is regulated centrally (in the brain) by hormone feedback loops that naturally occur after the placenta is delivered. Although traditionally, lactation occurs following pregnancy, lactation may also be induced with hormone therapy and nipple stimulation in the absence of pregnancy.
== Mechanisms == Evidence from physiological, pharmacological and neuroimaging studies suggest serotonin (also called 5-HT) may play a role in anorexia. While acutely ill, metabolic changes may produce a number of biological findings in people with anorexia that are not necessarily causative of the anorexic behavior. For example, abnormal hormonal responses to challenges with serotonergic agents have been observed during acute illness, but not recovery. Nevertheless, increased cerebrospinal fluid concentrations of 5-hydroxyindoleacetic acid (a metabolite of serotonin), and changes in anorectic behavior in response to acute tryptophan depletion (tryptophan is a metabolic precursor to serotonin) support a role in anorexia. The activity of the 5-HT2A receptors has been reported to be lower in patients with anorexia in a number of cortical regions, evidenced by lower binding potential of this receptor as measured by PET or SPECT, independent of the state of illness. While these findings may be confounded by comorbid psychiatric disorders, taken as a whole they indicate serotonin in anorexia. These alterations in serotonin have been linked to traits characteristic of anorexia such as obsessiveness, anxiety, and appetite dysregulation. Neuroimaging studies investigating the functional connectivity between brain regions have observed a number of alterations in networks related to cognitive control, introspection, and sensory function. Alterations in networks related to the dorsal anterior cingulate cortex may be related to excessive cognitive control of eating related behaviors.
Sources: en.wikipedia.org
Validation establishes suitability for a new method, while verification confirms that a method works in a specific laboratory. Verification is often used when a validated method is adopted with existing equipment and staff. Both rely on documented acceptance criteria.
Quantification usually compares detector response to a standard curve made from reference standards. The curve may be external, internal, or based on standard addition depending on matrix effects. Results are reported with units and, when required, uncertainty.
Carryover occurs when analyte from a previous injection remains in the system and appears in a later chromatogram. It can come from the injector, column, or tubing. Blank injections and needle washes help detect and reduce it.
Method validation is the documented process of showing that an HPLC procedure produces reliable results for a defined purpose. It examines parameters such as accuracy, precision, specificity, linearity, and robustness. Regulators and quality systems often require validation before routine use.